The actual information capacity of genetic regulatory elements depends on the absolute concentrations of the relevant molecules, on the time available for reading out the information, and on other details of the different noise sources in the system [1]}, [2]}. At one extreme, if the capacity is three bits, then a single regulatory element is sufficient to capture the full positional information. But if the capacity of a single element is only one bit, then we need multiple regulatory elements even in response to a single transcription factor.
<FIGURE>